Three general development problems are under investigation. 1. The objective of this research project is an understanding of the organized development of embryonic teeth. Experimental in vitro studies explore alterations in form of the developing tooth rudiment. The results of exposure to materials which modify the differentiation of tooth tissues and deposition of extracellular materials are studied histologically and cytologically. The in vitro behavior of isolated tooth tissues and their capabilities for differentiation are also investigated. 2. One major objective of study of secondary palate development of the mouse embryo is gauging the importance of epithelial-mesenchymal interactions for the differentiation of the component tissues of the palatal process. These in vitro studies are performed with isolated epithelium and mesenchyme from palatal processes. 3. Tissue factors bearing upon the ontogeny of trigeminal ganglion neurons are studied by organ culture combinations of embryonic ganglia and primitive organs and tissues from anatomically associated portions of the embryo's body. The cytological consequences of these associations are evaluated with the light and electron microscope in order to assess whether neurons and associated cells have reached morphological maturity.